Note that btrott's solution will assign an empty string to $source if the pattern doesn't match. You will need to test for that at some time. I prefer a regex like this:

my $quote = "";
if ($source =~ /last: ([0-9.]+)/i;) {
    $quote = $1;
} else {
    # do the Not Found Dance
}
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It's a matter of personal preference -- just don't neglect the check! Note also that the regex may run faster without the .* at the start (backtracking can be expensive).